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I have a side job with OhKeyCaps building mechanical keyboards. We use a amoeba single switch pcb which at the bare minimum (IE no rgb) requires a switch and a single 1n4148 diode. Fairly common stuff and easy to figure out. We've talked about having someone make us a flexible PCB to speed up the building process. So that is the problem at hand. We could easily just get some SMD diodes between each switch and the trace and be done.

Since I build keyboards all the times both my kids wanted a mechanical keyboard so I started them off with the iris. (Iris is just a brand and style of keyboard, not important to the question). When I got the PCB for the iris I noticed that there wasn't a multitude of diodes like I had expected from when I hand wire my keyboards. Instead there are 7 diodes installed and 28 switches per PCB half. I did some probing around and found that the diodes have 6 pins on it but the markings are too small for me to read. From what I can tell the IC is just 4 diodes configured like so: best guess at diode configuration

I'm not sure how the they all tie together but I know that the two cathodes eventually go to the controller (atmega32u4) in the end. I wanted to know how this could be accomplished so I started looking around with my limited knowledge on how to make said diode. I eventually found a small article which told me what I was searching for was diode array which then led me to digikey... but when I searched for a 7 segment common cathode I couldn't find one nor did I know how or where to search. The end game of this is that it is a hassle to wire up 70+ diodes on a keyboard and we have been talking about someone to make us a flexible pcb to simplify and speed up our building process, although making/building the flexible PCB is unrelated to my questions. I need to be able to find a solution before I present it to my boss so how do I google for buying a diode array, or does it have another name? My only requirements of the diode array is same size or smaller than the same number of 1n4148 diodes it is replacing, and that it isn't too small where I can't hand solder this. A nice to have would be that I can have a single chip to replace 6 diodes. I hope this edit clears up confusion

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  • \$\begingroup\$ I need help understanding what I'm looking at though, cause all of this is foreign to me. Like I know that my pro-micro atmega32u4 is 5v powered from usb, but all the other things about that made no sense. Also when I tried to filter down diode arrays for 6 diodes it came back with 0 results. I know very little about eletronics but am good at letting the blue smoke out \$\endgroup\$ – Robert Snyder Jun 4 '20 at 15:38
  • \$\begingroup\$ I did a search again with "Diode array" in search and refined it with 1n4148 and in stock and got back 0 results.. ugh I have no idea what i'm doing \$\endgroup\$ – Robert Snyder Jun 4 '20 at 15:45
  • \$\begingroup\$ You have left out a lot of important information. What is an "iris"? What do you mean by "the diodes have...4 diodes"? What else is on the board besides the diodes and switches? Do you know what a multiplexed keyboard is? \$\endgroup\$ – Elliot Alderson Jun 4 '20 at 16:53
  • \$\begingroup\$ Your question is not clear. Do you want to make a flexible PCB that duplicates the circuit of the 'iris'? _"Will I be able to hand solder this to flexible pcb?" - depends on the IC package. What package are you intending to use? \$\endgroup\$ – Bruce Abbott Jun 4 '20 at 18:49
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    \$\begingroup\$ You say it has four diodes, but then draw just two in your schematic. Which is it? \$\endgroup\$ – Hearth Jun 5 '20 at 12:53
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Diode arrays are pretty popular, and you can find them by searching in Digikey etc.

Here is one line-up of Schottky diode arrays from one manufacturer:

enter image description here

BAV70 and similar are regular switching diodes (not Schottky).

Machine-populated SMT 1N4148 diodes may be more economical and may have other advantages as well.

The below search is sufficient to constrain it to only 28 results out of almost 12,000. Further distinctions include package and Schottky vs. regular as well as manufacturer, price, stock level etc.

enter image description here

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  • \$\begingroup\$ I chatted with the digikey guys too after a few hours of digging around and he said I could use Schottky diodes. I'm not affraid to try, but is there any advantage disatvantage to using them? \$\endgroup\$ – Robert Snyder Jun 5 '20 at 16:43
  • \$\begingroup\$ looks like according to your pictures the one on the iris is the bas40dw-05.. cool :D I learned something \$\endgroup\$ – Robert Snyder Jun 5 '20 at 16:52
  • \$\begingroup\$ Schottky diodes have lower voltage drop so they should result in more noise margin, but are leakier so they might work better with lower resistor values, especially at high temperatures. \$\endgroup\$ – Spehro Pefhany Jun 5 '20 at 16:54
  • \$\begingroup\$ You can probably get 1N4148-equivalent switching diodes in the same configurations, I didn't bother to look. That's certainly the case with the ubiquitous SOT-23 configurations. \$\endgroup\$ – Spehro Pefhany Jun 5 '20 at 17:10
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I'm very much afraid that time and tide have passed you by. Surface mount is so prevalent, and has been for about 20 years, that there aren't very many through-hole products being developed - and this especially applies to diode arrays. And SMT products have been getting smaller and smaller, as you've noticed. Legacy through-holes are still common enough, but you take what you can get. (Power semiconductors are something of an exception, due to packaging/thermal issues, but that doesn't help you.)

Going to Digikey, search on "diode arrays", then select the top offering. Select "active" (of course, since you do want to buy some), and then "through hole" in "more filters". This will give you (at present) 2,643 possibilities. Apply filters.

Now look at the field labelled "Diode Configuration". You'll see that you only have 5 choices, none of them what you want.

Sorry, but you're out of luck.

Oh yes, and just for fun, select "7 independent". A 14-pin DIP package is quicker to install than bending 7 sets of diode leads and then installing one-by-one, right? You'll get 1 possibility. And, since that one costs $292 each in singles, I doubt that you'll be much interested.

The takeaway is that SMT rules, and if you want to produce electronics boards you're going to have to upgrade your skills and equipment to comply. This is not always true, of course; non-exotic op amp circuits can usually be realized by through-hole parts, and this includes things like amplifiers. But in your case, sticking with the devil you know means that you'll need to bend a lot of diode leads. The iris boards are showing you the way.

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  • \$\begingroup\$ yeah I wish we had the ability to use a traditional pcb, but the problem is the curvature of our boards (ohkeycaps.com/products/built-to-order-dactyl-manuform-keyboard). What is the difference between SMT and SMD? \$\endgroup\$ – Robert Snyder Jun 5 '20 at 16:44
  • \$\begingroup\$ @RobertSnyder SMD and SMT are two words for the same thing, essentially. \$\endgroup\$ – Hearth Jun 5 '20 at 17:18
  • \$\begingroup\$ @RobertSnyder - D stands for "device", and T stands for "technology". \$\endgroup\$ – WhatRoughBeast Jun 7 '20 at 18:04

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